1. Field of the Invention
The present invention relates to a zoom lens of plus-minus two-group structure. More particularly, the present invention relates to a zoom lens suited for a lens shutter type 35-mm compact camera.
2. Related Background Art
In recent years, zooming has rapidly been in progress even in the field of lens shutter type compact cameras. Thus, the various products with a zoom lens mounted thereon have been provided on the market, and with the cost in view, a zoom lens of the kind which can be constructed most simply and compactly with a plus-minus two-group structure has mainly been adopted.
Recently, in particular, the specification has increasingly become higher still and there has been proposed a zoom lens including a wide angle of view of approximately 62 degrees at the wide angle edge with a zooming ratio of more than double. In Japanese Patent Laid-Open Application No. 2-50118, for example, a zoom lens including a wide angle of view of approximately 62 degrees at the wide angle end with a zooming ratio of 2.83 times is proposed.
The two-group structure zoom lens disclosed in the above-mentioned Japanese Patent Laid-Open Application No. 2-50118 satisfies the specification provided by the present invention which will be described later as far as the wide angle of view and zooming ratio of the lenses are concerned. However, in order to meet the requirements for making the entire length of the lenses as short as strongly desired, the power of each of the lens groups are intensified. As a result, the second lens group is particularly constructed with four lenses, and the back focus is made as short as 1.4 mm-0.5 mm, so that the lens diameter of the last portion becomes as great as 32 mm-36 mm. As a lens of the kind, this diameter is considerably large. Hence, there are encountered the problems set forth below in assembling cameras actually by mounting this type of lens therein.
(a) It is difficult to secure the eccentric precision because large and heavy lenses of the second lens group should be moved in zooming.
(b) The large lenses of the second lens group are positioned close to the surface of the film, and the lenses should be machined to be oblong analogous to the picture frame of the film, leading to the difficulty in centering the lenses.
(c) The film surface and the lenses of the second lens group are placed extremely close to each other, and there is a considerable possibility that dust particles and the like adhering to the lenses can easily be taken into a picture. Furthermore, the ghost due to the reflections of the faces of film and lens can easily appear.
Further, in each of the embodiments disclosed in the Japanese Patent Laid-Open Application No. 2-50118, two to three aspherical faces are used in order to improve the focusing capability, and in addition, some of them employ a floating structure for the lens movement. Accordingly, any one of them is suitably adopted as a lens for the compact camera for which a severe restriction exists in costwise.